The aims of this project are: to study the development of the internal structural features and innervation of slow muscle fibers and to compare and contrast this with the development of twitch muscle fibers; to study the distribution and number of nerve terminals on the limb muscle fibers of newborn mammals; to study the role of the satellite-cell in degeneration and regeneration of muscle fibers by investigating the degenerative and regenerative processes of denervated and injured insect muscle fibers, which have no satellite cells (or, at least, very few); to correlate the ultrastructural features of synaptic vesicles with the transmitter substance present by studying the insect brain normally and experimentally; to investigate the source of the apparently independent motor nerve supply of glomus cells of the carotid body of the rat; to study the composition of the granulated vesicles inglomus cells of the carotid body by administration of drugs and to determine the site of uptake of these substances into glomus cells; to determine if there are retrograde effects influencing synaptic maturation by studying the development of the calyx on avian ciliary ganglion cells after experimental procedures. Electron microscopy and histochemical staining methods will be used. In the case of receptors, it is hoped to find the properties of these terminals by which they are able to transduce a specific stimulus into a nerve impulse. In the case of motor terminals, it is hoped to learn how these endings exert their influence upon the postsynaptic elements involved.